Climate change and South Dunedin flooding

Major flooding in South Dunedin last year is sometimes cited as a sign of future problems with climate change, but it isn’t a simple issue.

Last week the Commissioner for the Environment spoke in Dunedin, reported by the ODT in South Dunedin flood risk ‘an issue’:

‘‘The most troubling example of this in New Zealand, at least in the short term, is South Dunedin,” she said.

‘‘As the sea rises, that groundwater will rise higher and higher over time.”

Last June’s flood was an example of what was to come.

‘‘This flooding from underneath will become more and more of an issue.”

However, the warming of the oceans presented the greatest risk of flooding.

Much of South Dunedin is less than a metre above sea level. It is drained and reclaimed swamp (originally turned into market gardens by Chinese settlers). So obviously a potential rise in sea levels is a concern.

Last year’s floods occurred after the second worst rainfall since records began in 1918. It’s impossible to say if this event was a symptom of climate change or not.

But the causes of flooding were varied and some at least were due to local human effects and poor maintenance of drainage infrastructure. A just released report highlights some of these problems.

ODT: Mud-tank maintenance failure

A long-awaited report into last June’s flood has found 75% of mud tanks in South Dunedin were not properly maintained.

A Fulton Hogan spokeswoman said in a statement last night it was confident it fulfilled the requirements of the contract.‘‘Due to the age and historic nature of the stormwater network, including the mud tanks, effective maintenance is a challenge.”

The failure of drainage infrastructure has been talked about for a while.

And:

The report also raised longer-term issues about the state of South Dunedin’s infrastructure and said further work would be done to find out what investment was needed.

It found changes in South Dunedin meant the stormwater network, much of which was installed in the 1950s and 1960s, did not perform as well as intended when built.

This included the expansion of hard surfaces, which had increased the amount of rainfall that needed to be dealt with by the stormwater system from 45% to 60%.

And:

In a separate issue, it found the screen on the Portobello Rd pump station was unable to be cleared of debris due to the severity of the flood, an issue that would be fixed when modifications were made this year.

So whether the rainfall was a hundred year type weather event or a symptom of climate change there are a number of other factors involved.

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29 Comments

  1. Alan Wilkinson

     /  21st April 2016

    We got flooded,a decade ago die to poor (= non existent) maintenance of council drains. One factor was simple incompetence – a critical outlet had been blocked by the council drilling another pipe through it – only discovered when a camera was sent down. Another factor was RMA absurdities – regional councils requiring unaffordable consent processes for maintenance of thousands of ocean drain outlets.

    Reply
  2. Brown

     /  21st April 2016

    We all need to live in caves so Dunedin’s council can ignore infrastructure maintenance. Deluded morons are everywhere.

    Lower Hutt had its biggest recorded (as far as they recorded things in those days) flood in the late 19th century (believed to be at least twice the size of anything since). When it happens again they will blame climate change because more tax will stop nature doing what it does.

    Reply
  3. Zedd

     /  21st April 2016

    I heard there were two main reasons why the flooding was so bad:
    1) the weather system was stationary & most of the water flowed down from the hill suburbs
    2) the drains around Sth D were blocked up & water just sat on the surface

    I’ve still got a few pics, I took of my street, looking like a river & surrounding area looking like ‘Lake Sth D’ on 3-4 June.. I’m hoping this doesn’t become an annual event.. we shall see ! :/

    Come on all you ‘climate change deniers’.. tell me its just part of a cycle; not proof of any ongoing change 🙂 😦

    Reply
    • Alan Wilkinson

       /  21st April 2016

      I’ll happily tell you it’s not proof of any ongoing climate change. And neither is it proof it’s just part of a cycle. The only thing it is proof of is a failure by council to do its fundamental job of providing and maintaining drainage infrastructure. Probably too busy declaring itself GE free and opposing the TPP.

      Reply
      • Zedd

         /  21st April 2016

        @AW

        you keep believing it.. :/
        I invite you to come visit, IF it happens again this year ??? we shall see……. 😦

        Reply
        • Alan Wilkinson

           /  21st April 2016

          ‘‘Because the rainfall intensity exceeded the capacity of the system, even working at its best, for 17 whole hours.”

          “that was the second-most extreme rain event since records began in 1918”

          Design failure. Obviously not configured to cope even with much more frequent smaller events.

          Reply
  4. Maggy Wassilieff

     /  21st April 2016

    How convenient – blame climate change for incompetence and general bungling.

    Reply
    • Gezza

       /  21st April 2016

      Flooding of the township here last Winter (after an unparalled 3 days of heavy rain) was partially caused by uncleared blocked drains and council failure to adhere to the annual stream clearance programme. Mind you, the rain was also exceptionally heavy and the runoff was unprecedented. The stream beside me has never flooded anywhere near so high in the 9 years I’ve been here.

      Reply
  5. Zedd

     /  21st April 2016

    I’m actually more concerned about the huge decrease in Arctic sea ice & shrinking glaciers & ice sheets in Greenland & Antarctica. This will lead to sea-level rise.
    Some prediction say.. as much as 6 meters. my house in Sth Dn will be well submerged. BUT I may not be around to see it ? :/ 😦

    Go on tell me ‘its just normal’ (NOT !!)

    Reply
    • Alan Wilkinson

       /  21st April 2016

      Arctic sea ice makes no difference to sea level because it is anyway floating. There is a huge seasonal variation in it every year – far, far bigger than the decrease season to season.

      I’ll just tell you that the increase in sea level since the last ice age is slow, steady and normal. You and I won’t be around to see any change in that.

      Reply
      • Gezza

         /  21st April 2016

        One of the predictions that climate change is occurring is that storms and hurricanes will get more frequent and / or get much larger. However there is also a 25 year natural cycle of this kind of variation in Hurricane size and intensity, and while there have been some recent monsters, I’m not sure that they are yet at a point where they could be considered to have significantly deviated from the natural cycle.

        Chinese neighbours from Malaysia travel back there every 2 or 3 years to see family, and they tell me the growing season over there has changed. Fruit crops have sometimes rotted on the trees because the monsoon rains are coming now about month later, they said.

        Reply
    • Gezza

       /  21st April 2016

      Although I think measurements of sea level rise are only still at “noise” level, or arguable from place to place, I have been watching the retreat of glaciers worldwide, and the ongoing shrinkage of the extent of Arctic sea ice. I have read claims somewhere that satellites which can somehow measure the mass or thickness of the Antarctic ice show that this too is diminishing.
      http://ecowatch.com/2015/12/27/arctic-sea-ice-melt.

      Reply
      • Alan Wilkinson

         /  21st April 2016

        Here is the global total polar ice area:

        And the individual poles:

        Honestly, you have to wonder about the climate alarmism as soon as you look at the data.

        Reply
        • Gezza

           /  21st April 2016

          It’s not the area that’s diminishing so much as the mass or thickness, apparently Alan. That video clip in the article linked shows that, I think, in that while the area covered is vacillating, the apparent density (from the colour) is reducing.
          Also, I think glacial retreat worldwide is unprecedented in historical times. Our own
          Franz Joseph and Fox glaciers have retreated significantly since early last century.
          https://en.wikipedia.org/wiki/Glaciers_of_New_Zealand

          Reply
          • Alan Wilkinson

             /  21st April 2016

            I just don’t think that is credible from the above area charts, Gezza. Also even the alarmists make their Antarctic claims specific to localised areas, mostly the peninsular.

            Yes, alpine glaciers have been melting since the last ice age and will no doubt continue to do so as the planet gradually warms by about 1 deg C per century.

            Reply
            • Gezza

               /  21st April 2016

              You may understand the science better than I, Alan, and there are usually useful but complex arguments from commenters on this site, but this page explains what I have seen and heard about Antarctic ice change.

            • Alan Wilkinson

               /  21st April 2016

              I don’t read that website, Gezza. It is an alarmist vehicle run by an alarmist fanatic, John Cook. I prefer to look directly at the data collected by objective science studies.

            • Alan Wilkinson

               /  21st April 2016

              … you can do that directly using the pure science resources linked from here:

              https://wattsupwiththat.com/reference-pages/

              No need to filter through anyone’s interpretation or selective reporting.

            • @AW

              I hear that the warming will not occur on a slow, steady graph.. BUT a sudden jump. I saw a news report that showed that temperatures over the poles are rising more rapidly than other areas (5degs in recent years) because ice reflects the sun’s rays back to space.. sea water does not.

              I agree with Gezza; its not necassarily the surface area that is the most noticeable decrease.. BUT the thickness of the ice, which satelitte images have confirmed are shrinking/getting thinner.

              BUT be my guest.. ignore it, I hope your house is more than 6 meters above the current high tide mark :/

            • Alan Wilkinson

               /  21st April 2016

              Actually I think clouds reflect the sun better than ice. As for ice thickness, it is a lot easier to measure extent so I would be far more confident that the latter measurements are accurate than the former.

              Arctic temperatures:
              ftp://ftp.ssmi.com/msu/graphics/tlt/plots/rss_ts_channel_tlt_northern%20polar_land_and_sea_v03_3.png

              Antarctic temperatures
              ftp://ftp.ssmi.com/msu/graphics/tlt/plots/rss_ts_channel_tlt_southern%20polar_land_and_sea_v03_3.png

              Be my guest, ignore the facts if you wish.

            • Gezza

               /  21st April 2016

              Thanks Alan. I do look at articles on Wattsupwiththat. As a non-scientist unfamiliar with some of the specialist details I have the usual problem that, while other sites may have data and details from climate alarmists Watts is a climate sceptic so his interpretations of data will differ from his competitors’. I do believe globally the ice sheets are losing mass.

              However sea level rise is not happening as quickly and uniformly as the majority of climate scientists predict, and I’m aware a lot of temperature, sea level, and other satellite data are/were subject to adjustments in attempts to get comparative consistency between old data measured differently,or that was altered by changes in satellite calibrations etc, and that this opens the main climate change monitoring agencies like NOAA up for questions as to its reliability and interpretation.

              I’m not able to reach any conclusions, so I just try to keep a loose track on the competing arguments and read the commentaries & graphs where the arguments get too technical for me.

            • Alan Wilkinson

               /  21st April 2016

              Excellent, Gezza. Keep your eyes on the data and you can’t go wrong.

              The articles on Wattsupwiththat are of variable quality as are the comments, but they do at least allow free debate unlike almost all of the alarmist websites so nonsense generally gets challenged and sometimes completely rubbished.

              However the data sources linked from it are excellent.

  6. Zedd

     /  21st April 2016

    @AW

    TOUCHE ! 😀

    Reply
    • Zedd

       /  21st April 2016

      BUT having said that.. I often find that some of the ‘scientific evidence’ put about to either prove or debunk something.. can be manipulated (to meet certain agendas or Financial interests) take the so-called ‘evidence’ that Cannabis CAUSES mass insanity, blood lust & leads all users onto HARD drugs ! believe it or not……………… :/

      Reply
      • Alan Wilkinson

         /  21st April 2016

        Always check out the data, Zedd. Usually it is a lot more honest than its reporters.

        Reply
      • Gezza

         /  21st April 2016

        That’s true, it’s bollocks Zedd. Never mind cannabis I went straight into the hard stuff as soon as I left school. Booze.

        Reply
  7. Brown

     /  21st April 2016

    See AW – facts get a down tick, bullshit gets an uptick. Democracy is clearly a bloody dangerous concept with so many fuckwits that can vote.

    Reply

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